Motor drive device including current detector

ABSTRACT

A motor drive device includes a power conversion unit configured to supply a drive current to a motor, a current detector configured to detect a current flowing from the power conversion unit into the motor, an A/D converter configured to convert the current detected by the current detector into digital data and outputs the digital data, a motor control unit configured to control the drive current supplied from the power conversion unit to the motor, using the digital data output from the A/D converter, and a sampling adjustment unit configured to adjust a sampling operation of the A/D converter performed for the current detected by the current detector, in accordance with the response time taken after the current detector detects the current until the A/D converter outputs the digital data of the current.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a motor drive device including acurrent detector.

2. Description of the Related Art

In a motor drive device which drives motors in a machine tool, forgingmachinery, an injection molding machine, industrial machinery, or anindustrial robot, the speed, the torque, or the rotor position of anymotor is instructed and controlled for the motor provided for each driveaxis. In such a motor drive device, it is important to accurately detectthe current flowing through the windings of any motor, by a currentdetection circuit including a current detector and an A/D(Analog-to-Digital) converter. The current in the windings of the motordetected by the current detector is converted into digital data by theA/D converter and used for motor drive control. As a current detectionscheme for such a current detector, a current detector using a shuntresistor or a Hall element, for example, is available. As a conversionscheme for an A/D converter which converts the current detected by thecurrent detector into digital data, a successive approximation A/Dconverter or a ΔΣ modulation A/D converter, for example, is available.

As disclosed in, e.g., Japanese Unexamined Patent Publication (Kokai)No. H07-298674, a noise suppression method for suppressing the influenceof noise mixed during detection upon obtaining the average value of thelatest measured value and N (≥1) previous measured values obtained bydetection at a predetermined sampling timing is known to set a lowerlimit value and an upper limit value, based on the present averagevalue, determine whether the latest detected value falls within a rangebetween the lower limit value and the upper limit value, employ thelatest detected value as a latest measured value when the latestdetected value falls within the range, and redo detection by discardingthe latest detected value when the latest detected value falls outsidethe range.

As disclosed in, e.g., WO 13/084289, a power conversion device is knownto include an inverter circuit which includes a parallel combination ofseries-connected switching element pairs corresponding to the respectivephases of a multiphase AC motor and allows each phase voltage fordriving the motor to be extracted from a connection point between theswitching elements in each series-connected switching element pair, acurrent detection resistor connected in series with each of theseries-connected switching element pairs, a current detection means fordetecting a current flowing through the motor, for each phase, an A/Dconversion means, provided in the current detection means, forconverting a current detection signal detected by the current detectionmeans into a digital signal and performing current value detectionprocessing, a control unit which outputs a drive signal for performingPWM control of each switching element of the inverter circuit, based ona duty ratio set value or a voltage command value of a voltage appliedto each phase of the motor, and a current detection phase selectionmeans for selecting the current detection signal detected by each of thecurrent detection means and controlling a timing of the current valuedetection processing by the A/D conversion means, wherein the currentdetection phase selection means determines the timing of the currentvalue detection processing by the A/D conversion means in one period ofa PWM pulse that is a carrier for the PWM control, based on the voltagecommand value or the duty ratio set value.

As disclosed in, e.g., Japanese Unexamined Patent Publication (Kokai)No. 2015-171215, a motor control device which performs ON/OFF control ofa plurality of switching elements connected in a three-phase bridgeconfiguration, in accordance with a predetermined PWM signal pattern, todrive a motor via an inverter circuit which converts a direct currentinto a three-phase alternating current is known to include a currentdetection element which is connected to a DC side of the invertercircuit and generates a signal corresponding to a current value, a rotorposition determination means for determining a rotor position, based ona phase current of the motor, a PWM signal generation means forgenerating a three-phase PWM signal pattern to follow the rotorposition, and a current detection means for detecting the phase currentof the motor, based on the PWM signal pattern and the signal generatedby the current detection element, wherein the PWM signal generationmeans changes a duty in both a retard direction and an advance directionwith reference to an arbitrary phase in a carrier period, for a firstphase of the three-phase PWM signal pattern, changes the duty in onedirection of the retard direction and the advance direction withreference to an arbitrary phase in the carrier period, for a secondphase, and changes the duty in a direction opposite to the one directionwith reference to an arbitrary phase in the carrier period, for a thirdphase, and the device further includes a timing adjustment means for,when the current detection means detects a two-phase current at a timingfixed in the carrier period of the PWM signal and becomes incapable ofdetecting the two-phase current at the fixed timing, adjusting adetection timing to allow detection of a current at a variable timingcorresponding to a magnitude of a voltage output to the invertercircuit, for at least one phase.

As disclosed in, e.g., Japanese Unexamined Patent Publication (Kokai)No. 2013-062985, a rotating electrical machine control device whichdetects an actual current flowing through a rotating electrical machineand controls the rotating electrical machine by performing currentfeedback control to bring the actual current close to a target currentfor the rotating electrical machine is known to include a samplingperiod setting unit which sets a sampling period in which a detectedcurrent is obtained by sampling the actual current containing an ACfrequency component, a current sampling unit which obtains the detectedcurrent by sampling the actual current in accordance with the samplingperiod, and a current control unit which performs the current feedbackcontrol, based on the detected current and the target current, uponsetting of a response region to make a response to input of a frequencycomponent in a predetermined frequency region, wherein the samplingperiod setting unit sets the sampling period in accordance with arotation speed of the rotating electrical machine so that at least oneof a plurality of aliasing frequencies of the detected current detecteddue to aliasing falls outside the response region of the current controlunit.

As disclosed in, e.g., Japanese Unexamined Patent Publication (Kokai)No. 2012-110074, a current detection device which detects a currentoutput from a multiphase inverter using triangular wave pulse widthmodulation is known to include a current detection means for detecting acurrent for each of a plurality of specific timings in a given periodset in advance, and an addition means for summing current detectionvalues for each of the plurality of specific timings in the givenperiod, wherein the current detection means detects the current at leastonce on each of a leading edge and a trailing edge of a carrier of thetriangular wave PWM, as the plurality of specific timings in the givenperiod.

As disclosed in, e.g., Japanese Unexamined Patent Publication (Kokai)No. 2010-252595, a motor drive device including current feedback controlbased on PWM control, using a current detector which detects a motorcurrent, is known to include a carrier signal generator which outputs atriangular wave carrier signal, a motor current detector which detectsan average current value in a given interval, a current detection timinggenerator which outputs a current detection trigger with reference tothe carrier signal, a current controller which performs current controlto make the average current value detected by the motor current detectorfollow a current command value and updates a voltage command value at apeak and a trough of the carrier signal, and a PWM controller whichreceives the carrier signal and the voltage command value and outputs aPWM signal to an inverter unit, wherein a period of the peak and thetrough of the carrier signal is matched with a time of the giveninterval in which the average current value is detected.

SUMMARY OF INVENTION

With the development of technology regarding parts constituting acurrent detection circuit located in a motor drive device, the responsecharacteristic (response speed) of a current detection circuit whichdetects a current by a current detector and outputs digital data by anA/D converter is improving, and the response time taken after currentdetection until digital data output is increasingly shortening. In newlydesigning, maintaining, or retrofitting a motor drive device, theresponse characteristic of current detection is improved using a latestcurrent detection circuit, to improve any type of motor controllabilitysuch as the motor acceleration and deceleration time, feed smoothness,or motor output.

When a plurality of current detection circuits located in the motordrive device or current detection circuits before and after replacementhave a difference in response characteristic (response speed) in theperiod after current detection until digital data output, the currentdetection value converted into digital data output from the currentdetection circuit varies even for the same current magnitude. Thedifference in response characteristic (response speed) occurs betweenthe current detection circuits due to, e.g., the difference in currentdetection scheme based on whether a current detector uses a shuntresistor or a Hall element, the difference in performance based onwhether the current detector uses an old or new model, or thedifferences between individual parts (part-related variations)constituting the current detector. For example, the response time isshorter (the response speed is higher) in a current detector using ashunt resistor than in a current detector using a Hall element. Further,upon a comparison even between current detectors of the same detectionscheme, the response time is shorter (the response speed is higher) in anew model than in an old model. When a current detection value convertedinto digital data having variations for each such current detectioncircuit is used for current control in the motor drive device, thisadversely affects the motor controllability.

In replacing a current detection circuit used for the motor drivedevice, the compatibility of response time (response speed) is oftenimportant before and after replacement. When, for example, variouscircuits (e.g., a current control unit and a power conversion circuit)in the motor drive device are used as in the conventional technique, andonly a current detection circuit is replaced, a current detectioncircuit including a conventional current detector having a long responsetime (low response speed) is more preferable than a current detectioncircuit including a latest current detector having a short response time(high response speed), in terms of maintaining a given motorcontrollability. However, the conventional current detector or currentdetection circuit may no longer be manufactured and may be alreadyunavailable. Further, a current detection circuit including a latestcurrent detector may be superior in, e.g., cost, size, thermalresistance, or humidity resistance to a current detection circuitincluding a conventional current detector, and in such a case, the useof the conventional current detection circuit by placing importance onmaintenance of a given motor controllability is inefficient from acomprehensive viewpoint.

It is, therefore, desired to implement a motor drive device capable ofmaintaining a given motor controllability independently of thedifference in response characteristic of a current detection circuitincluding a current detector and an A/D converter.

According to one aspect of the present disclosure, a motor drive deviceincludes a power conversion unit configured to supply a drive current toa motor, a current detector configured to detect a current flowing fromthe power conversion unit into the motor, an A/D converter configure toconvert the current detected by the current detector into digital dataand outputs the digital data, a motor control unit configured to controlthe drive current supplied from the power conversion unit to the motor,using the digital data output from the A/D converter, and a samplingadjustment unit configured to adjust a sampling operation of the A/Dconverter performed for the current detected by the current detector, inaccordance with a response time taken after the current detector detectsthe current until the A/D converter outputs the digital data of thecurrent.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood with reference tothe following accompanying drawings:

FIG. 1 is a block diagram illustrating a motor drive device according toone embodiment;

FIG. 2A is a graph for explaining the relationship between the actualcurrent flowing from a power conversion unit into a motor and thecurrent detected by a current detector in a successive approximation A/Dconverter and illustrates an exemplary waveform of the current detectedby the current detector;

FIG. 2B is a graph for explaining the relationship between the actualcurrent flowing from the power conversion unit into the motor and thecurrent detected by the current detector in the successive approximationA/D converter and illustrates an enlarged view of a portion bounded by adotted line in the waveform of the detected current illustrated in FIG.2A;

FIG. 2C is a graph for explaining the relationship between the actualcurrent flowing from the power conversion unit into the motor and thecurrent detected by the current detector in the successive approximationA/D converter and schematically illustrates the relationship with theactual current in an enlarged view of a portion bounded by a dotted linein the waveform of the detected current illustrated in FIG. 2B;

FIG. 3 is a graph for explaining adjustment of a sampling operation by asampling adjustment unit according to a first mode when thecharacteristics of a current detector having a long response time arematched with those of a current detector having a short response time;

FIG. 4 is a graph for explaining adjustment of a sampling operation bythe sampling adjustment unit according to the first mode when thecharacteristics of a current detector having a short response time arematched with those of a current detector having a long response time;

FIG. 5 is a graph schematically illustrating the relationship betweenthe actual current flowing from a power conversion unit into a motor andthe current detected by a current detector in a ΔΣ modulation A/Dconverter;

FIG. 6 is a graph for explaining adjustment of a sampling operation by asampling adjustment unit according to a second mode when thecharacteristics of a current detector having a long response time arematched with those of a current detector having a short response time;

FIG. 7 is a graph for explaining adjustment of a sampling operation bythe sampling adjustment unit according to the second mode when thecharacteristics of a current detector having a short response time arematched with those of a current detector having a long response time;

FIG. 8A is a graph illustrating an exemplary relationship between theinductance of the motor and the ripple of the current detected by thecurrent detector and exemplifies the case where the inductance of themotor is low; and

FIG. 8B is a graph illustrating an exemplary relationship between theinductance of the motor and the ripple of the current detected by thecurrent detector and exemplifies the case where the inductance of themotor is high.

DETAILED DESCRIPTION

A motor drive device including a current detector will be describedbelow with reference to the drawings. These drawings use differentscales as appropriate to facilitate an understanding. The modeillustrated in each drawing is one example for carrying out the presentinvention, and the present invention is not limited to the embodimentsillustrated in these drawings.

FIG. 1 is a block diagram illustrating a motor drive device according toan embodiment of the present disclosure. The case where a motor 2 isdriven by a motor drive device 1 will be taken as an example herein.Machines equipped with the motor 2 include, e.g., a machine tool, arobot, forging machinery, an injection molding machine, industrialmachinery, various electrical appliances, an electric train, anautomobile, and an aircraft. The type of motor 2 is not intended toparticularly limit this embodiment, and the motor 2 may serve as a DCmotor or an AC motor. The number of motors 2 is not intended toparticularly limit this embodiment, either. Referring to FIG. 1, for thesake of simplicity, only one pair of a current detector 12 and an A/Dconverter 13 is provided, but a plurality of pairs of current detectors12 and A/D converters 13 may be provided in accordance with, e.g., thetype of motor 2 or the method for controlling the motor 2. When, forexample, the motor 2 serves as a three-phase AC motor, pairs of currentdetectors 12 and A/D converters 13 are provided for two or all of thethree phases. When, for example, the motor 2 serves as a single-phase ACmotor, a current detector 12 and an A/D converter 13 are provided foreach phase. When, for example, the motor 2 serves as a DC motor, acurrent detector 12 and an A/D converter 13 are provided on, e.g., acathode-side power supply line.

The motor drive device 1 according to one embodiment that drives themotor 2 includes a power conversion unit 11, a current detector 12, anA/D converter 13, a motor control unit 14, and a sampling adjustmentunit 15. The current detector 12 and the A/D converter 13 constitute acurrent detection circuit 20.

The power conversion unit 11 is controlled based on a command from themotor control unit 14 and supplies a drive current to the motor 2. Whenthe motor 2 serves as an AC motor, the power conversion unit 11includes, e.g., a rectifier configured to convert AC power supplied froman AC power supply into DC power, and an inverter configured to convertthe DC power into AC power and supplies AC drive power to the motor 2.Alternatively, for example, the power conversion unit 11 is implementedas an inverter configured to convert DC power supplied from a batteryinto AC power and supplies AC drive power to the motor 2. When the motor2 serves as a DC motor, the power conversion unit 11 is implemented as,e.g., a rectifier configured to convert AC power supplied from an ACpower supply into DC power and supplies a DC drive current to the motor2, or a DC/DC converter configured to convert a DC voltage applied froma battery into an appropriate DC voltage and supplies a DC drive currentto the motor 2. The configuration of the power conversion unit 11defined herein is merely illustrative, and the configuration of thepower conversion unit 11 may be defined including terms such as a powersupply or a battery.

The current detector 12 detects a current flowing from the powerconversion unit 11 into the motor 2. As a current detection scheme forthe current detector 12, a current detector using a shunt resistor or aHall element, for example, is available. An analog signal related to thecurrent detected by the current detector 12 is input to the A/Dconverter 13.

The A/D converter 13 converts the analog signal related to the currentdetected by the current detector 12 into digital data and outputs thedigital data. The A/D converter 13 performs sampling processing fortaking the amplitude values of a continuous analog signal related to thecurrent detected by the current detector 12 with discrete periods(sampling periods), quantization processing for approximating theamplitude values taken with the discrete periods by discrete amplitudevalues, and encoding processing for converting the discrete amplitudevalues into codes represented by binary values: “0” and “1.” As ananalog-to-digital conversion scheme for the A/D converter 13, asuccessive approximation A/D converter and a ΔΣ modulation A/Dconverter, for example, are available. Digital data related to thecurrent output from the A/D converter 13 is input to the motor controlunit 14.

The motor control unit 14 controls a drive current supplied from thepower conversion unit 11 to the motor 2, using the digital data outputfrom the A/D converter 13. More specifically, the following operation isperformed: The motor control unit 14 generates a current command basedon the speed (speed feedback) of the motor 2 detected by a speeddetector (not illustrated) and a predetermined speed command for themotor 2, in accordance with an operation program for the motor 2. Thecurrent control unit 21 in the motor control unit 14 generates a commandfor controlling the speed, the torque, or the rotor position of themotor 2, based on the current command and digital data (currentfeedback) related to the current flowing into the motor 2 and input fromthe A/D converter 13. The power conversion unit 11 is controlled basedon the command from the motor control unit 14 and supplies a drivecurrent to the motor 2. With this operation, the motor 2 has its speed,torque, or rotor position controlled based on the drive current suppliedfrom the power conversion unit 11. The configuration of the motorcontrol unit 14 defined herein is merely illustrative, and theconfiguration of the motor control unit 14 may be defined includingterms such as a position command generation unit, a speed command unit,a torque command generation unit, and a switching command generationunit.

The sampling adjustment unit 15 adjusts a sampling operation of the A/Dconverter 13 performed for the current detected by the current detector12, in accordance with the response time (response characteristic) takenafter the current detector 12 detects a current until the A/D converter13 outputs digital data of the current. The response time taken afterthe current detector 12 detects a current until the A/D converter 13outputs digital data of the current represents the responsecharacteristic of the current detector 12 of the current detectioncircuit 20 including the current detector 12 and the A/D converter 13,and the current detector 12 exhibits a better response characteristicfor a shorter response time. Since a filter unit (not illustrated) andthe like are placed in the input stage of the A/D converter 13, the“response time (response characteristic) of the current detector 12” ismore specifically defined as the “summed response time (responsecharacteristic) of the response time (response characteristic) of thecurrent detector 12 and the response times (response characteristics) ofthe filter unit and the like placed in the output stage of the currentdetector 12.” In this specification, for the sake of simplicity, the“response times (response characteristics) of the current detector 12and the succeeding filter unit and the like” will be simply referred toas the “response time (response characteristic) of the current detector12.” The response characteristic of the current detector 12 can berepresented by the response speed in place of the response time. Theresponse speed of the current detector 12 is defined as the processingspeed of the current detector 12 until the current detected by thecurrent detector 12 is encoded into digital data and output by the A/Dconverter 13. According to this definition, the higher the responsespeed of the current detector 12, the better the response characteristicof the current detector 12. The operation of the sampling adjustmentunit 15 will be described in detail later.

The above-mentioned motor control unit 14 and sampling adjustment unit15 may be constructed in, e.g., software program form, and in this case,the function of each unit is implemented by causing an arithmeticprocessing device in the motor drive device 1 to operate the softwareprogram. Alternatively, the function of the sampling adjustment unit 15may be implemented by mounting in, e.g., an existing motor drive device,a semiconductor integrated circuit in which a software program forimplementing the function of the sampling adjustment unit 15 is written.

The operation of the sampling adjustment unit 15 will be subsequentlydescribed in more detail, individually for the case (first mode) wherethe A/D converter 13 serves as a successive approximation A/D converterand the case (second mode) where the A/D converter 13 serves as a ΔΣmodulation A/D converter.

FIG. 2A is a graph for explaining the relationship between the actualcurrent flowing from a power conversion unit into a motor and thecurrent detected by a current detector in a successive approximation A/Dconverter and illustrates an exemplary waveform of the current detectedby the current detector. FIG. 2B is a graph for explaining therelationship between the actual current flowing from the powerconversion unit into the motor and the current detected by the currentdetector in the successive approximation A/D converter and illustratesan enlarged view of a portion bounded by a dotted line in the waveformof the detected current illustrated in FIG. 2A. FIG. 2C is a graph forexplaining the relationship between the actual current flowing from thepower conversion unit into the motor and the current detected by thecurrent detector in the successive approximation A/D converter andschematically illustrates the relationship with the actual current in anenlarged view of a portion bounded by a dotted line in the waveform ofthe detected current illustrated in FIG. 2B.

Due to the difference in response characteristic (detection rate) of thecurrent detector 12, the detected current output from the currentdetector 12 varies for the same actual current. The current detector 12,for example, has a shorter response time (higher response speed) when ituses a shunt resistor than when it uses a Hall element. As illustratedin FIG. 2C, for the waveform of the same actual current, the waveform(indicated by an alternate long and short dashed line in FIG. 2C) of acurrent detector 12 having a long response time is delayed in timecompared to the waveform (indicated by a broken line in FIG. 2C) of acurrent detector 12 having a short response time. When the responsecharacteristic (detection rate) of the current detector 12 varies inthis manner, the successive approximation A/D converter 13 placed in theoutput stage of the current detector 12 performs a sampling operation atthe same timing (time t₀), and the current value of digital data outputfrom the A/D converter 13 varies depending on the difference in responsecharacteristic (detection rate) of the current detector 12. In view ofthis, the sampling adjustment unit 15 according to the first modecorresponding to the case where the A/D converter 13 serves as asuccessive approximation A/D converter adjusts the period in which thesampling timing of the A/D converter 13 is set, so that the currentvalue of identical digital data is stably output from the A/D converter13 for the same actual current, independently of the difference inresponse characteristic (detection rate) of the current detector 12.

The sampling adjustment unit 15 according to the first modecorresponding to the case where the A/D converter 13 serves as asuccessive approximation A/D converter performs adjustment to change theperiod in which the sampling timing of the successive approximation A/Dconverter 13 is set for the current detected by the current detector 12,in accordance with the response time taken after the current detector 12detects a current until the A/D converter 13 outputs digital data of thecurrent. More specifically, the sampling adjustment unit 15 according tothe first mode performs adjustment to temporally delay the samplingtiming when the response time is longer than a predetermined target timeand performs adjustment to temporally advance the sampling timing whenthe response time is shorter than the target time, so that digital dataidentical to that obtained when sampling is performed at a samplingtiming set in correspondence with the target time is output from the A/Dconverter 13. When the response characteristic of the current detector12 is represented by the “response speed” in place of the “responsetime,” the “target time” can be represented by the “target speed.”

FIG. 3 is a graph for explaining adjustment of a sampling operation by asampling adjustment unit according to the first mode when thecharacteristics of a current detector having a long response time arematched with those of a current detector having a short response time.When the response time taken after the current detector 12 detects acurrent until the A/D converter 13 outputs digital data of the currentis longer than a predetermined target time, the sampling adjustment unit15 according to the first mode performs adjustment to delay the periodin which the sampling timing is set, so that digital data identical tothat obtained when sampling is performed at a sampling timing set incorrespondence with the target time is output from the successiveapproximation A/D converter 13. The case where, for example, a currentdetection circuit 20 including a current detector 12 having a longresponse time (low response speed) is adjusted so that digital dataidentical to that obtained by a current detector having a short responsetime (high response speed) is output from the current detection circuit20 corresponds to this adjustment example. In other words, the responsetime in a current detector having a short response time corresponds tothe above-mentioned “target time,” and an A/D converter 13 in a currentdetection circuit 20 including a current detector 12 having a longresponse time corresponds to the target to be adjusted by the samplingadjustment unit 15 according to the first mode. As illustrated in, e.g.,FIG. 3, the sampling adjustment unit 15 is used to delay the samplingtiming of an A/D converter 13 in a current detection circuit 20including a current detector 12 having a long response time to beadjusted from original time t₁ until time t₂ that is the sampling timingof an A/D converter in a current detection circuit having a shortresponse time, so that a current value I_(A) of digital data identicalto that obtained by the A/D converter in the current detection circuitincluding the current detector having a short response time is outputfrom the A/D converter 13 in the current detection circuit 20 includingthe current detector 12 having a long response time to be adjusted, forthe value of the same actual current (I_(A) in FIG. 3).

The duration from time t₁ to time t₂ corresponds to the amount ofadjustment applied by the sampling adjustment unit 15 according to thefirst mode to the A/D converter 13 in the current detection circuit 20including the current detector 12 having a long response time to beadjusted. Since the current detection rate is higher in a shunt resistortype current detector than in a Hall element type current detector,when, for example, the characteristics of a shunt resistor type currentdetector 12 are matched with those of a Hall element type currentdetector, the sampling adjustment unit 15 according to the first modedelays the period in which the sampling timing of the successiveapproximation A/D converter 13 placed in the output stage of the shuntresistor type current detector 12 is set, to match this sampling timingwith that of the ΔΣ modulation A/D converter 13 placed in the outputstage of the shunt resistor type current detector.

FIG. 4 is a graph for explaining adjustment of a sampling operation bythe sampling adjustment unit according to the first mode when thecharacteristics of a current detector having a short response time arematched with those of a current detector having a long response time.When the response time taken after the current detector 12 detects acurrent until the A/D converter 13 outputs digital data of the currentis shorter than a predetermined target time, the sampling adjustmentunit 15 according to the first mode performs adjustment to advance theperiod in which the sampling timing is set, so that digital dataidentical to that obtained when sampling is performed at a samplingtiming set in correspondence with the target time is output from thesuccessive approximation A/D converter 13. The case where, for example,a current detection circuit 20 including a current detector 12 having ashort response time (high response speed) is adjusted so that digitaldata identical to that obtained by a current detector having a longresponse time (low response speed) is output from the current detectioncircuit 20 corresponds to this adjustment example. In other words, theresponse time in a current detector having a long response timecorresponds to the above-mentioned “target time,” and an A/D converter13 in a current detection circuit 20 including a current detector 12having a short response time corresponds to the target to be adjusted bythe sampling adjustment unit 15 according to the first mode. Asillustrated in, e.g., FIG. 4, the sampling adjustment unit 15 is used todelay the sampling timing of an A/D converter 13 in a current detectioncircuit 20 including a current detector 12 having a short response timeto be adjusted from original time t₃ until time t₄ that is the samplingtiming of an A/D converter in a current detection circuit including acurrent detector having a long response time, so that a current valueI_(B) of digital data identical to that obtained by the A/D converter inthe current detection circuit including the current detector having along response time is output from the A/D converter 13 in the currentdetection circuit 20 including the current detector 12 having a shortresponse time to be adjusted, for the value of the same actual current(I_(B) in FIG. 3). The duration from time t₃ to time t₄ corresponds tothe amount of adjustment applied by the sampling adjustment unit 15according to the first mode to the A/D converter 13 in the currentdetection circuit 20 including the current detector 12 having a shortresponse time to be adjusted. Since the current detection rate is higherin a shunt resistor type current detector than in a Hall element typecurrent detector, when, for example, the characteristics of a Hallelement type current detector 12 are matched with those of a shuntresistor type current detector, the sampling adjustment unit 15according to the first mode advances the period in which the samplingtiming of the successive approximation A/D converter 13 placed in theoutput stage of the Hall element type current detector 12 is set, tomatch this sampling timing with that of the ΔΣ modulation A/D converter13 placed in the output stage of the Hall element type current detector.

FIG. 5 is a graph schematically illustrating the relationship betweenthe actual current flowing from a power conversion unit into a motor andthe current detected by a current detector in a ΔΣ modulation A/Dconverter. In the ΔΣ modulation A/D converter 13, since analog data in acertain sampling interval is averaged and then analog-to-digitalconverted, digital data output from the ΔΣ modulation A/D converter 13is limited to that in the sampling interval of the current valuedetected by the current detector 12. As already described above, due tothe difference in response characteristic (detection rate) of thecurrent detector 12, the detected current output from the currentdetector 12 varies for the same actual current. When the responsecharacteristic (detection rate) of the current detector 12 varies inthis manner, the ΔΣ modulation A/D converter 13 placed in the outputstage of the current detector 12 obtains different analog data even inthe same sampling interval and, in turn, obtains different averagevalues of the analog data in this sampling interval, so that the currentvalue of digital data output from the A/D converter 13 varies dependingon the difference in response characteristic (detection rate) of thecurrent detector 12. In view of this, the sampling adjustment unit 15according to the second mode corresponding to the case where the A/Dconverter 13 serves as a ΔΣ modulation A/D converter adjusts the periodin which the sampling interval of the A/D converter 13 is set, so thatthe current value of identical digital data is stably output from theA/D converter 13, independently of the difference in responsecharacteristic (detection rate) of the current detector 12.

The sampling adjustment unit 15 according to the second modecorresponding to the case where the A/D converter 13 serves as a ΔΣmodulation A/D converter performs adjustment to change the period inwhich the sampling interval of the ΔΣ modulation A/D converter 13 is setfor the current detected by the current detector 12, in accordance withthe response time taken after the current detector 12 detects a currentuntil the A/D converter 13 outputs digital data of the current. Morespecifically, the sampling adjustment unit 15 according to the secondmode performs adjustment to temporally delay the sampling interval whenthe response time is longer than a predetermined target time andperforms adjustment to temporally advance the sampling interval when theresponse time is shorter than the target time, so that digital dataidentical to that obtained when sampling is performed in a samplinginterval set in correspondence with the target time is output from theA/D converter 13.

FIG. 6 is a graph for explaining adjustment of a sampling operation by asampling adjustment unit according to the second mode when thecharacteristics of a current detector having a long response time arematched with those of a current detector having a short response time.When the response time taken after the current detector 12 detects acurrent until the A/D converter 13 outputs digital data of the currentis longer than a predetermined target time, the sampling adjustment unit15 according to the second mode performs adjustment to delay the periodin which the sampling interval is set, so that digital data identical tothat obtained when sampling is performed at a sampling timing set incorrespondence with the target time is output from the ΔΣ modulation A/Dconverter 13. The case where, for example, a current detection circuit20 including a current detector 12 having a long response time (lowresponse speed) is adjusted so that digital data identical to thatobtained by a current detection circuit including a current detectorhaving a short response time (high response speed) is output from thecurrent detection circuit 20 corresponds to this adjustment example. Inother words, the response time in a current detection circuit includinga current detector having a short response time corresponds to theabove-mentioned “target time,” and an A/D converter 13 in a currentdetection circuit 20 including a current detector 12 having a longresponse time corresponds to the target to be adjusted by the samplingadjustment unit 15 according to the second mode. As illustrated in,e.g., FIG. 6, the sampling adjustment unit 15 is used to delay thesampling interval of an A/D converter 13 in a current detection circuit20 including a current detector 12 having a long response time to beadjusted until the same time as the sampling interval of an A/Dconverter in a current detection circuit including a current detectorhaving a short response. time, so that a current value of digital dataidentical to that obtained by the A/D converter in the current detectioncircuit including the current detector having a short response time isoutput from the A/D converter 13 in the current detection circuit 20including the current detector 12 having a long response time to beadjusted, for the value of the same actual current. The time obtained bydelaying the sampling interval corresponds to the amount of adjustmentapplied by the sampling adjustment unit 15 according to the second modeto the A/D converter 13 in the current detection circuit 20 includingthe current detector 12 having a long response time to be adjusted.When, for example, the characteristics of a shunt resistor type currentdetector 12 are matched with those of a Hall element type currentdetector, the sampling adjustment unit 15 according to the second modedelays the period in which the sampling interval of the successiveapproximation A/D converter 13 placed in the output stage of the shuntresistor type current detector 12 is set, to match this samplinginterval with that of the ΔΣ modulation A/D converter 13 placed in theoutput stage of the shunt resistor type current detector.

FIG. 7 is a graph for explaining adjustment of a sampling operation bythe sampling adjustment unit according to the second mode when thecharacteristics of a current detector having a short response time arematched with those of a current detector having a long response time.When the response time taken after the current detector 12 detects acurrent until the A/D converter 13 outputs digital data of the currentis shorter than a predetermined target time, the sampling adjustmentunit 15 according to the second mode performs adjustment to advance theperiod in which the sampling interval is set, so that digital dataidentical to that obtained when sampling is performed at a samplingtiming set in correspondence with the target time is output from the ΔΣmodulation A/D converter 13. The case where, for example, a currentdetection circuit 20 including a current detector 12 having a shortresponse time (high response speed) is adjusted so that digital dataidentical to that obtained by a current detection circuit including acurrent detector having a long response time (low response speed) isoutput from the current detection circuit 20 corresponds to thisadjustment example. In other words, the response time in a currentdetector having a long response time corresponds to the above-mentioned“target time,” and an A/D converter 13 in a current detection circuit 20including a current detector 12 having a short response time correspondsto the target to be adjusted by the sampling adjustment unit 15according to the second mode. As illustrated in, e.g., FIG. 7, thesampling adjustment unit 15 is used to delay the sampling interval of anA/D converter 13 in a current detection circuit 20 including a currentdetector 12 having a short response time to be adjusted until the sametime as the sampling interval of an A/D converter in a current detectioncircuit including a current detector having a long response time, sothat a current value of digital data identical to that obtained by theA/D converter in the current detection circuit including the currentdetector having a long response time is output from the A/D converter 13in the current detection circuit 20 including the current detector 12having a short response time to be adjusted, for the value of the sameactual current. The time obtained by advancing the sampling intervalcorresponds to the amount of adjustment applied by the samplingadjustment unit 15 according to the second mode to the A/D converter 13in the current detection circuit 20 including the current detector 12having a short response time to be adjusted. When, for example, thecharacteristics of a Hall element type current detector 12 are matchedwith those of a shunt resistor type current detector, the samplingadjustment unit 15 according to the second mode advances the period inwhich the sampling interval of the successive approximation A/Dconverter 13 placed in the output stage of the Hall element type currentdetector 12 is set, to match this sampling interval with that of the ΔΣmodulation A/D converter placed in the output stage of the Hall elementtype current detector.

FIG. 8A is a graph illustrating an exemplary relationship between theinductance of the motor and the ripple of the current detected by thecurrent detector and exemplifies the case where the inductance of themotor is low. FIG. 8B is a graph illustrating an exemplary relationshipbetween the inductance of the motor and the ripple of the currentdetected by the current detector and exemplifies the case where theinductance of the motor is high.

For the waveform of the same actual current, the waveform (indicated byalternate long and short dashed lines in FIGS. 8A and 8B) of a currentdetector 12 having a long response time is delayed in time compared tothe waveform (indicated by broken lines in FIGS. 8A and 8B) of a currentdetector 12 having a short response time, and when the responsecharacteristic (detection rate) of the current detector 12 varies inthis manner, the current value of digital data output from an A/Dconverter 13 (a successive approximation A/D converter in the exampleillustrated in FIGS. 8A and 8B) placed in the output stage of thecurrent detector 12 varies depending on the difference in responsecharacteristic (detection rate) of the current detector 12, even in thesame sampling time (time t₀). The same applies to the ΔΣ modulation A/Dconverter 13. As illustrated in FIGS. 8A and 8B, the lower theinductance of the motor 2, the larger the ripple of a current flowingfrom the power conversion unit 11 into the motor 2 detected by thecurrent detector 12, and therefore the lower the inductance of the motor2, the larger the difference in current value of digital data outputfrom the A/D converter 13 between a current detector 12 having a longresponse time and a current detector 12 having a short response time.Accordingly, the lower inductance of the motor 2 allows more effectiveadjustment of the sampling operation of the A/D converter 13 by thesampling adjustment unit 15.

The amount of adjustment applied by the sampling adjustment unit 15according to each of the above-mentioned first and second modes to theA/D converter 13 in the current detection circuit 20 to be adjusted isset in the following way. For example, the same actual current can bedetected by each of a current detection circuit 20 to be adjusted and acurrent detection circuit (i.e., a current detection circuit having atarget response time; to be referred to as a “target current detectioncircuit” hereinafter) having characteristics with which thecharacteristics of the current detection circuit 20 to be adjusted aredesirably matched, the current value of digital data output from thecurrent detection circuit 20 to be adjusted can be compared with that ofdigital data output from the target current detection circuit, and a“temporal shift” in sampling timing or sampling interval of the A/Dconverter 13 which allows a match between these current values can befound out and set as the above-mentioned “amount of adjustment.”Alternatively, a comparison may be made in motor controllability, e.g.,acceleration and deceleration time, and a “temporal shift” in samplingtiming or sampling interval which allows a match between their valuesmay be found out and set as the above-mentioned “amount of adjustment.”The “amount of adjustment” may even be obtained by an experiment. Oragain, the “amount of adjustment” may be obtained by an adjustmentamount calculation circuit (not illustrated) including a current sourcewhich supplies the same actual current to the current detection circuit20 to be adjusted and the target current detection circuit, and anarithmetic circuit which compares the current value of digital dataoutput from the current detection circuit 20 to be adjusted with that ofdigital data output from the target current detection circuit and findsout by arithmetic processing a “temporal shift” in sampling timing orsampling interval of the A/D converter 13 which allows a match betweenthese current values. The adjustment amount calculation circuit, forexample, compares the current value of digital data output from thecurrent detection circuit 20 to be adjusted with that of digital dataoutput from the target current detection circuit, while delaying oradvancing, as appropriate, the period in which the sampling timing orthe sampling interval is set in the A/D converter 13 to be adjusted,finds out a “temporal shift” when the deviation obtained as a result ofcomparison is minimized (preferably zero), and sets it as the “amount ofadjustment.” The amount of adjustment set by an experiment or theadjustment amount calculation circuit is input to the samplingadjustment unit 15, which performs adjustment to change the samplingtiming (in a successive approximation A/D converter) or the samplinginterval (in a ΔΣ modulation A/D converter) of the A/D converter 13 inthe current detection circuit 20 to be adjusted, based on the inputamount of adjustment.

As described above, with the motor drive device according to thisembodiment, even when a plurality of current detectors located in themotor drive device or current detectors before and after replacementhave a difference in response characteristic (response time or responsespeed) in the period after current detection until digital data output,since the sampling adjustment unit is used to perform adjustment tochange the sampling timing (in a successive approximation A/D converter)or the sampling interval (in a ΔΣ modulation A/D converter) of an A/Dconverter in a current detection circuit including a current detector tobe adjusted, variations in current detection value converted intodigital data output from each current detection circuit can be keptless. Since the current control unit in the motor control unit of themotor drive device according to this embodiment performs current controlusing a current detection value converted into digital data, with lessvariations output from each current detection circuit, a given motorcontrollability can be maintained independently of the difference inresponse characteristic of a current detection circuit including acurrent detector and an A/D converter.

In the motor drive device according to this embodiment, in replacing acurrent detection circuit used for the motor drive device, the currentdetection circuit can even be easily adjusted by placing importance onthe compatibility of response time (response speed) before and afterreplacement. When, for example, various circuits (e.g., a currentcontrol unit and a power conversion circuit) in the motor drive deviceare used as in the conventional technique, and only a current detectioncircuit is replaced with one including a latest current detectorsuperior in, e.g., cost, size, thermal resistance, or humidityresistance and having a short response time (high response speed), sincethe sampling adjustment unit is used to perform adjustment to change thesampling timing (in a successive approximation A/D converter) or thesampling interval (in a ΔΣ modulation A/D converter) of an A/D converterin a current detection circuit to be adjusted, so that a current valueconverted into digital data identical to that obtained by a currentdetection circuit including a conventional current detector having along response time (low response speed) is output for the same actualcurrent, a given compatibility of response time (response speed) of thecurrent detection circuit before and after replacement can bemaintained, and a given motor controllability can, in turn, bemaintained.

One aspect of the present disclosure can implement a motor drive devicecapable of maintaining a given motor controllability independently ofthe difference in response characteristic of a current detection circuitincluding a current detector and an A/D converter.

1. A motor drive device comprising: a power conversion unit configuredto supply a drive current to a motor; a current detector configured todetect a current flowing from the power conversion unit into the motor;an A/D converter configured to convert the current detected by thecurrent detector into digital data and outputs the digital data; a motorcontrol unit configured to control the drive current supplied from thepower conversion unit to the motor, using the digital data output fromthe A/D converter; and a sampling adjustment unit configured to adjust asampling operation of the A/D converter performed for the currentdetected by the current detector, in accordance with a response timetaken after the current detector detects the current until the A/Dconverter outputs the digital data of the current.
 2. The motor drivedevice according to claim 1, wherein the A/D converter comprises asuccessive approximation A/D converter, and the sampling adjustment unitperforms adjustment to change a period in which a sampling timing of thesuccessive approximation A/D converter is set for the current detectedby the current detector, in accordance with the response time.
 3. Themotor drive device according to claim 2, wherein when the response timeis longer than a predetermined target time, the sampling adjustment unitperforms adjustment to delay the period in which the sampling timing isset, so that digital data identical to digital data obtained whensampling is performed at a sampling timing set in correspondence withthe target time is output from the successive approximation A/Dconverter.
 4. The motor drive device according to claim 2, wherein whenthe response time is shorter than a predetermined target time, thesampling adjustment unit performs adjustment to advance the period inwhich the sampling timing is set, so that digital data identical todigital data obtained when sampling is performed at a sampling timingset in correspondence with the target time is output from the successiveapproximation A/D converter.
 5. The motor drive device according toclaim 1, wherein the A/D converter comprises a ΔΣ modulation A/Dconverter, and the sampling adjustment unit performs adjustment tochange a period in which a sampling interval of the ΔΣ modulation A/Dconverter is set for the current detected by the current detector, inaccordance with the response time.
 6. The motor drive device accordingto claim 5, wherein when the response time is longer than apredetermined target time, the sampling adjustment unit performsadjustment to delay the period in which the sampling interval is set, sothat digital data identical to digital data obtained when sampling isperformed in a sampling interval set in correspondence with the targettime is output from the ΔΣ modulation A/D converter.
 7. The motor drivedevice according to claim 5, wherein when the response time is shorterthan a predetermined target time, the sampling adjustment unit performsadjustment to advance the period in which the sampling interval is set,so that digital data identical to digital data obtained when sampling isperformed in a sampling interval set in correspondence with the targettime is output from the ΔΣ modulation A/D converter.
 8. The motor drivedevice according to claim 4, wherein the current detector comprises ashunt resistor.
 9. The motor drive device according to claim 3, whereinthe current detector comprises a Hall element.